Rom 9:6 Not as though the word of God hath taken none effect. For they [are] not all Israel, which are of Israel:
7 Neither, because they are the seed of Abraham, [are they] all children: but, In Isaac shall thy seed be called.
8 That is, They which are the children of the flesh, these [are] not the children of God: but the children of the promise are counted for the seed.
Gal 3:16 Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.
Gen 15:5 And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be.
6 And he believed in the LORD; and he counted it to him for righteousness.
Gal 3:28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
29 And if ye [be] Christ's, then are ye Abraham's seed, and heirs according to the promise.
Gal 4:22 For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
23 But he [who was] of the bondwoman was born after the flesh; but he of the freewoman [was] by promise.
24 Which things are an allegory: for these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar.
25 For this Agar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children.
26 But Jerusalem which is above is free, which is the mother of us all.
27 For it is written, Rejoice, [thou] barren that bearest not; break forth and cry, thou that travailest not: for the desolate hath many more children than she which hath an husband.
28 Now we, brethren, as Isaac was, are the children of promise.
29 But as then he that was born after the flesh persecuted him [that was born] after the Spirit, even so [it is] now.
30 Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman.
31 So then, brethren, we are not children of the bondwoman, but of the free.
Gen 15:18 In the same day the LORD made a covenant with Abram, saying, Unto thy seed have I given this land, from the river of Egypt unto the great river, the river Euphrates:
Gen 17:4 As for me, behold, my covenant [is] with thee, and thou shalt be a father of many nations.
Gen 17:7 And I will establish my covenant between me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee.
Gen 17:8 And I will give unto thee, and to thy seed after thee, the land wherein thou art a stranger, all the land of Canaan, for an everlasting possession; and I will be their God.
9 And God said unto Abraham, Thou shalt keep my covenant therefore, thou, and thy seed after thee in their generations.
10 This [is] my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised.
Gen 17:18 And Abraham said unto God, O that Ishmael might live before thee!
19 And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, [and] with his seed after him.
20 And as for Ishmael, I have heard thee: Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation.
Gen 21:9 And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking.
10 Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, [even] with Isaac.
11 And the thing was very grievous in Abraham's sight because of his son.
12 And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.
The scripture is clear that the "seed" who is referenced in the Abrahamic promises (which include the land) is Jesus Christ. So this inheritance is to Christ and those who are in Christ. The scripture talks about Abraham being the father of many nations (not one nation - the nation of Israel) but it talks about Ishmael being the father of ONE nation with 12 princes. This is an allegory for the 12 tribes of Israel.